1. Field of the Invention
This invention relates to nonvolatile memory devices. More specifically, the invention is a nonvolatile analog memory and method of using same to store and retrieve analog data.
2. Description of the Related Art
There is a continuing need to increase the density of memory storage devices. The number of bytes per square centimeter is of great importance to digital device manufacturers as is the ability to retain the stored data without power being applied thereto. Currently, data is stored in a digital fashion with digital data typically being stored in CMOS circuits, RAM circuits, FLASH memory circuits, or ferroelectric memory circuits.
Standard CMOS digital memory is static and utilizes six transistors to store 1-bit of data. Dynamic RAM can store 1-bit using only three transistors, but these transistors must be refreshed every few milliseconds. Further, both static and dynamic RAM are volatile and cannot store data without power being applied thereto. For nonvolatile memory applications, FLASH memory is the most widely used technology as it can store 1-bit of data using a single transistor. However, FLASH memory is limited to use as an offline data storage device because the time it takes to write data thereto is considerably longer than the time required to write to other conventional memory devices. Furthermore, FLASH memory has a finite number of “write” cycles associated therewith thereby making FLASH memory an impractical choice for the dynamic storage of computer data. Ferroelectric memory is developing technology that currently is used to store 1-bit per cell.
While analog storage circuits are known, storing data in analog fashion has not been generally accepted as a viable alternative to digital data storage since analog signals usually disappear whenever power is removed from an analog storage circuit. Although ferroelectric transistors have shown promise as a means to store an analog signal for a relatively long period of time, the voltage stored on current ferroelectric transistors (i.e., indicative of the analog signal) experiences some voltage decay over time thereby negating the value of ferroelectric transistors as a building block for nonvolatile memory.